1. Field of the Invention
The present invention relates to a heteroepitaxial growth method for gallium nitride on a substrate.
Priority is claimed on Japanese Patent Application No 2004-071593, filed Mar. 12, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
Research for nitride compounds of gallium nitride (GaN) as a blue light emitting device material is advancing. Recently, a blue light emitting diode, which emits very bright light, has been developed and has been commercialized.
However, since it is difficult to produce single bulk crystals of gallium nitride having excellent crystalline properties, gallium nitride is subjected to heteroepitaxial growth on other materials such as sapphire, and thereby a thin film is prepared.
Specifically, a preparation method for single crystal nitride semiconductor is suggested in Japanese Unexamined Patent Application, First Publication No. H8-264439. The preparation method comprises the steps of making the surface temperature of a sapphire substrate high, and supplying nitrogen alone, and thereby a uniform nitrided surface is prepared. After that, while maintaining the nitrided surface at a relative low temperature, cationic elements such as gallium are deposited uniformly. Then, when nitrogen is supplied while the nitrided surface is maintained at a high temperature again, the surface is nitrided, and excess cationic elements are evaporated again. Due to this, bonding between cationic elements and nitrogen atoms is promoted, and a homogeneous initial layer of nitride semiconductors is prepared.
According to Japanese Unexamined Patent Application, First Publication No. H8-264439, a single crystal nitride semiconductor which is prepared by forming single crystal gallium nitride on a sapphire substrate has excellent crystalline properties.
In order to grow such single crystal gallium nitride having excellent crystalline properties, it is necessary to grown a buffer layer such as GaAlN, AlN, and the like at a low temperature, and then to grown GaN.
Nitride semiconductors can be used not only for blue light emitting diode material, but also fluorescent material which is excited by a light source for emitting ultraviolet light or electrons of FED (field luminescence display), and the like.
In these cases, it is considered that optical properties are more important than crystalline properties. Optical properties are evaluated by irradiating electrons on the nitride semiconductor, and mining cathode luminescence (CL).
In Japanese Unexamined Patent Application, First Publication No. H8-264439, the obtained gallium nitride is a single crystal. When the present inventors examined the strength of cathode luminescence (CL) of the obtained gallium nitride, CL strength was somewhat weak, and there was a problem that optical properties are insufficient.
In addition, since expensive material such as a sapphire substrate is used in conventional methods, there is a problem of cost.
In consideration of the above-described problems, an object of the present invention is to provide a heteroepitaxial growth method for gallium nitride which can prepare gallium nitride, which contains good quality fine crystals and has excellent optical properties, on a quartz substrate or a silicon substrate.